The present invention relates to vehicular transmissions and, more particularly, to vehicular transmissions having both electrical and mechanical drive paths to provide split-mode operation within the transmission between an input shaft and an output shaft.
The electrically-variable transmission (EVT) has been proposed for vehicles to improve fuel economy and reduce emissions. The EVT splits mechanical power between an input shaft and an output shaft into a mechanical power path and an electrical power by means of differential gearing. The mechanical power path may include clutches and additional gears. The electrical power path may employ two electrical power units, each of which may operate as a motor or as a generator. With an electric storage battery, the EVT can be incorporated into a propulsion system for a hybrid electric vehicle.
The hybrid vehicle or hybrid propulsion system uses an electrical power source, such as batteries, as well as an engine power source. The batteries are connected with the electrical drive units through an electronic control unit (ECU), which distributes the electrical power as required. The ECU also has connections with the engine and vehicle to determine operating characteristics, or operating demand, so that the electrical power units are operated properly as either a motor or a generator. When operating as a generator, the electrical power unit accepts power from either the vehicle or the engine and stores power in the battery, or provides that power to operate another electrical device or another electrical power unit on the vehicle or on the transmission.
There have been a number of electrically-variable transmissions proposed for vehicle operation. Examples of proposed electrically-variable transmissions are shown in U.S. Pat. No. 5,558,589 issued to Schmidt on Sep. 24, 1996, and assigned to the assignee of the present invention; U.S. Pat. No. 6,090,005 issued to Schmidt et al. on Jul. 18, 2000, and assigned to the assignee of the present invention; and U.S. Pat. No. 5,931,757 issued to Schmidt on Aug. 3, 1999, and assigned to the assignee of the present invention. The above-identified U.S. Pat. No. 5,931,757 defines the structure and operation of a variable two-mode, input-split, electro-mechanical transmission for a parallel hybrid electric propulsion system. The U.S. Pat. No. 5,558,589 discloses a two-mode, compound-split, electro-mechanical vehicular transmission, and U.S. Pat. No. 5,558,595 issued to Schmidt et al. on Sep. 24, 1996, discloses a one-mode, input-split transmission. These, and many other patents, describe various electrically-variable type transmissions.
One of the benefits of having an electrically-variable transmission incorporating more than one mode of operation is that each mode of operation will generally incorporate at least one mechanical point where one of the electrical power units is stationary, thereby reducing the electrical power input and providing a pure mechanical power flow path which is, of course, more efficient than a pure electrical power flow path.
Other hybrid type power transmissions are shown in U.S. Pat. No. 5,571,058 issued to Schmidt on Nov. 5, 1996; U.S. Pat. No. 5,577,973 issued to Schmidt on Nov. 26, 1996; U.S. Pat. No. 5,558,173 issued to Sherman on Sep. 24, 1996; and U.S. Pat. No. 5,558,175 issued to Sherman on Sep. 24, 1996, all of which are assigned to the assignee of the present invention.
It is an object of the present invention to provide an improved three-mode, input-split and compound-split electrically-variable transmission.
In one aspect of the present invention, the electrically-variable transmission has an input-split first mode of operation.
In another aspect of the present invention, the electrically-variable transmission has a compound-split mode during the second mode of operation.
In still another aspect of the present invention, the electrically-variable transmission has another compound-split power path during a third mode of operation.
In yet still another aspect of the present invention, the electrically-variable transmission incorporates a mechanical power source, two electrical power units, and three planetary gear sets.
In a further aspect of the present invention, the electrically-variable transmission incorporates four torque-transmitting mechanisms that are selectively engageable to provide the three modes of operation.
In yet a further aspect of the present invention, the four torque-transmitting mechanisms are operated in combinations of two to provide the three modes of operation.
In yet still a further aspect of the present invention, the electrically-variable transmission has a neutral condition with two of the torque-transmitting mechanisms engaged, wherein the transmission can operate in either the forward mode or a reverse mode from the neutral condition depending on the speed of one of the electrical power units.